From: Simon Pilgrim Date: Fri, 24 Feb 2017 17:46:18 +0000 (+0000) Subject: [APInt] Add APInt::extractBits() method to extract APInt subrange X-Git-Url: https://granicus.if.org/sourcecode?a=commitdiff_plain;h=30e6a76a6a9f6e2814ff46ee4bd61969d1ae58b9;p=llvm [APInt] Add APInt::extractBits() method to extract APInt subrange The current pattern for extract bits in range is typically: Mask.lshr(BitOffset).trunc(SubSizeInBits); Which can be particularly slow for large APInts (MaskSizeInBits > 64) as they require the allocation of memory for the temporary variable. This is another of the compile time issues identified in PR32037 (see also D30265). This patch adds the APInt::extractBits() helper method which avoids the temporary memory allocation. Differential Revision: https://reviews.llvm.org/D30336 git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@296141 91177308-0d34-0410-b5e6-96231b3b80d8 --- diff --git a/include/llvm/ADT/APInt.h b/include/llvm/ADT/APInt.h index 32fed77098c..fa4233a0aa9 100644 --- a/include/llvm/ADT/APInt.h +++ b/include/llvm/ADT/APInt.h @@ -1272,6 +1272,9 @@ public: /// as "bitPosition". void flipBit(unsigned bitPosition); + /// Return an APInt with the extracted bits [bitPosition,bitPosition+numBits). + APInt extractBits(unsigned numBits, unsigned bitPosition) const; + /// @} /// \name Value Characterization Functions /// @{ diff --git a/lib/Support/APInt.cpp b/lib/Support/APInt.cpp index 8ddbbe3a70d..f0c8f6be433 100644 --- a/lib/Support/APInt.cpp +++ b/lib/Support/APInt.cpp @@ -618,6 +618,38 @@ void APInt::flipBit(unsigned bitPosition) { else setBit(bitPosition); } +APInt APInt::extractBits(unsigned numBits, unsigned bitPosition) const { + assert(0 < numBits && "Can't extract zero bits"); + assert(bitPosition < BitWidth && (numBits + bitPosition) <= BitWidth && + "Illegal bit extraction"); + + unsigned loBit = whichBit(bitPosition); + if (isSingleWord()) + return APInt(numBits, VAL >> loBit); + + unsigned loWord = whichWord(bitPosition); + unsigned hiWord = whichWord(bitPosition + numBits - 1); + + // Single word result extracting bits from a single word source. + if (loWord == hiWord) + return APInt(numBits, pVal[loWord] >> loBit); + + // Extracting bits that start on a source word boundary can be done + // as a fast memory copy. + if (loBit == 0) + return APInt(numBits, makeArrayRef(pVal + loWord, 1 + hiWord - loWord)); + + // General case - shift + copy source words into place. + APInt Result(numBits, 0); + uint64_t *pDst = Result.pVal; + for (unsigned word = loWord; word < hiWord; ++word, ++pDst) { + uint64_t w0 = pVal[word + 0]; + uint64_t w1 = pVal[word + 1]; + *pDst = (w0 >> loBit) | (w1 << (APINT_BITS_PER_WORD - loBit)); + } + return Result.clearUnusedBits(); +} + unsigned APInt::getBitsNeeded(StringRef str, uint8_t radix) { assert(!str.empty() && "Invalid string length"); assert((radix == 10 || radix == 8 || radix == 16 || radix == 2 || diff --git a/lib/Target/X86/X86ISelLowering.cpp b/lib/Target/X86/X86ISelLowering.cpp index 618d7a8c561..348f8308099 100644 --- a/lib/Target/X86/X86ISelLowering.cpp +++ b/lib/Target/X86/X86ISelLowering.cpp @@ -5207,8 +5207,8 @@ static bool getTargetConstantBitsFromNode(SDValue Op, unsigned EltSizeInBits, EltBits.resize(NumElts, APInt(EltSizeInBits, 0)); for (unsigned i = 0; i != NumElts; ++i) { - APInt UndefEltBits = UndefBits.lshr(i * EltSizeInBits); - UndefEltBits = UndefEltBits.zextOrTrunc(EltSizeInBits); + unsigned BitOffset = i * EltSizeInBits; + APInt UndefEltBits = UndefBits.extractBits(EltSizeInBits, BitOffset); // Only treat an element as UNDEF if all bits are UNDEF. if (UndefEltBits.isAllOnesValue()) { @@ -5223,7 +5223,7 @@ static bool getTargetConstantBitsFromNode(SDValue Op, unsigned EltSizeInBits, if (UndefEltBits.getBoolValue() && !AllowPartialUndefs) return false; - APInt Bits = MaskBits.lshr(i * EltSizeInBits).zextOrTrunc(EltSizeInBits); + APInt Bits = MaskBits.extractBits(EltSizeInBits, BitOffset); EltBits[i] = Bits.getZExtValue(); } return true; @@ -6421,7 +6421,7 @@ static Constant *getConstantVector(MVT VT, const APInt &SplatValue, SmallVector ConstantVec; for (unsigned i = 0; i < NumElm; i++) { - APInt Val = SplatValue.lshr(ScalarSize * i).trunc(ScalarSize); + APInt Val = SplatValue.extractBits(ScalarSize, ScalarSize * i); Constant *Const; if (VT.isFloatingPoint()) { assert((ScalarSize == 32 || ScalarSize == 64) && diff --git a/lib/Target/X86/X86ShuffleDecodeConstantPool.cpp b/lib/Target/X86/X86ShuffleDecodeConstantPool.cpp index 41ad0971461..c24b74f7480 100644 --- a/lib/Target/X86/X86ShuffleDecodeConstantPool.cpp +++ b/lib/Target/X86/X86ShuffleDecodeConstantPool.cpp @@ -77,8 +77,8 @@ static bool extractConstantMask(const Constant *C, unsigned MaskEltSizeInBits, RawMask.resize(NumMaskElts, 0); for (unsigned i = 0; i != NumMaskElts; ++i) { - APInt EltUndef = UndefBits.lshr(i * MaskEltSizeInBits); - EltUndef = EltUndef.zextOrTrunc(MaskEltSizeInBits); + unsigned BitOffset = i * MaskEltSizeInBits; + APInt EltUndef = UndefBits.extractBits(MaskEltSizeInBits, BitOffset); // Only treat the element as UNDEF if all bits are UNDEF, otherwise // treat it as zero. @@ -88,8 +88,7 @@ static bool extractConstantMask(const Constant *C, unsigned MaskEltSizeInBits, continue; } - APInt EltBits = MaskBits.lshr(i * MaskEltSizeInBits); - EltBits = EltBits.zextOrTrunc(MaskEltSizeInBits); + APInt EltBits = MaskBits.extractBits(MaskEltSizeInBits, BitOffset); RawMask[i] = EltBits.getZExtValue(); } diff --git a/unittests/ADT/APIntTest.cpp b/unittests/ADT/APIntTest.cpp index 39a88cdca90..e8923b6ac01 100644 --- a/unittests/ADT/APIntTest.cpp +++ b/unittests/ADT/APIntTest.cpp @@ -1434,6 +1434,18 @@ TEST(APIntTest, isMask) { } } +TEST(APIntTest, extractBits) { + APInt i32(32, 0x1234567); + EXPECT_EQ(0x3456, i32.extractBits(16, 4)); + + APInt i256(256, -16776961 /* 0xFFFFFFFFFFFFFFFFFFFFFFFFFF0000FF */, true); + EXPECT_EQ(255, i256.extractBits(16, 0)); + EXPECT_EQ(127, i256.extractBits(16, 1)); + EXPECT_EQ(-1, i256.extractBits(32, 64).getSExtValue()); + EXPECT_EQ(-1, i256.extractBits(128, 128).getSExtValue()); + EXPECT_EQ(-8388481, i256.extractBits(128, 1).getSExtValue()); +} + #if defined(__clang__) // Disable the pragma warning from versions of Clang without -Wself-move #pragma clang diagnostic push